Filament positioning means for electron discharge devices



Jan. 5, 1960 BASSETT 2,920,226

FILAMENT POSITIONING MEANS FOR ELECTRON DISCHARGE DEVICES Filed Feb. 5, 1957 /Nl EN7'0R MARGARET BASSETT Isa waf TTORNE Y United States Patent FILAlVIENT POSITIONING MEANS FOR ELECTRON DISCHARGE DEVICES Margaret 'Bassett, Boston, Mass, assignor to Raytheon Company, a corporation 'of Delaware Application February 5, 1957, Serial No. 638,405 4 Claims. (Cl. 313-275) use in electron tubes having very close filament to grid-.

spacing requirements.

In this invention there is disclosed a half spacer having a straight edge for contacting a filament, thereby locating said filament at a position determined by the physical dimensions of said half spacer. In practicing the teachings of this invention, a separate half spacer is added to either or both of the two main spacers normally used in an electron tube for supporting the anode, control grid, screen grid and the suppressor grid. In the preferred embodiment, a pair of half spacers, constructed according to the teachings of this invention, are each placed one above the upper spacer and one below the lower spacer. The defined straight edge on said half spacers is accurately located with respect to the vertical supports for both the control grid and the screen grid thereby accurately positioning the filament with respect to the control grid. The defined straight edge on said half spacers is on a center line passing through the center of said vertical grid supports. For certain applications only a single half spacer may be needed for locatingthe filament depending on the inside diameter of the control grid.

The benefits to be derived from this invention will be more easily realized when considering the size of the control grid in tubes wherein this invention is particularly adaptable. For example, in a representativetube with the control grid in place, it is necessary, during the assembling process of the tube, for an operator to thread the filament wires through a centrally located opening in the upper main spacer, then between the control surfaces or laterals of said control grid, and then through a similarly located central opening in the lower main spacer. A satisfactory arrangement for centering a single filament and particularly multi-strand filaments between the laterals of the control grid has been the use of a spacer slot essentially rectangular in shape wherein one side of the slot is on the major center line of the control grid or slightly offset to take into consideration the filament diameter. This system has been used on both miniature and subminiature tubes and is particularly useful for centering two or more strands. As requirements became more stringent requiring closer and closer filament to grid spacings, this construction became a problem since grid diameters between laterals came down to the order of .010 inch and since the spacer slot edge is on the center line of the grid, there is left only approximately .005 inch for the filament connectors which are approximately .004 inch diameter to drop through. Nevertheless, millions of tubes were made in high production with this technique and with these spacings. When another increase in requirements demanded even smaller grid dimensions of the order of .006 inch and .008 inch with only .003 inch and .004 inch spacings left between one Q in the first stages of construction;

set of grid laterals and the spacer centering edge, it was no longer possible to insert and drop filaments through these openings in the conventional way. This invention provides an opening in the main spacers which allows a space equal to the full inside grid diameter size for filament connectors to slide through, since the slot in the main spacer now has its sides equidistant from the center line of the control grid and screen grid, if any. This invention provides the means for locating the filament without changing the dimensions of the central opening in the main spacers.

Further objects and advantages of this invention will be made more apparent as the description progresses, reference now being made to the accompanying drawings wherein:

Fig. 1 illustrates a side view of the electrode assembly Fig. 2 illustrates the top view of Fig. 1 taken along lines 2-2;

Fig. 3 illustrates the electrode subassembly in the second stage of assembly including the filament supports and the filament;

Fig. 4 illustrates the third stage of assembly for the electrode subassembly, which now includes a half spacer adjacent the uppermost main spacer and a half spacer.

adjacent the lowermost main spacer;

Fig. 5 illustrates a top view of Fig. 4 taken along lines 55; and,

Fig. 6 illustrates a sectional view of the glass envelope showing the completed electrode assembly for a completed electron tube.

Referring now to Fig. 1, there is shown an electrode subassembly 10 consisting of a top spacer 11 and a bottom spacer 12 supporting an anode structure 13 and 13, suppressor grids 14 and 14, a control grid not shown in this figure, and a screen grid 15.

Referring now to Fig. 2, which is a top view of the electrode subassembly 10, illustrated in Fig. 1, there is shown, at a greatly magnified scale, top spacer 11 and triangular openings 16 and 16 for the anode supports, which extend therethrough, and triangular openings 17 and 17 for the suppressor grid supports, which extend therethrough. The suppressor grids, as referred to and used herein, refer to deflector or beam-forming plates that serve and act as suppressors and hence, the term suppressor grids refers also to the beam-forming plates illustrated. Posts 18 support the screen grid laterals, and posts 19 support the control grid laterals. Located centrally on spacer 11 is a central opening 20 constructed in the form of a rectangle throughwhich the filament wires must be threaded. It can be seen that the largest opening of central opening 20 through which the filament wires will be threaded is limited by the distance between opposing surfaces 21 and 22 of the control grid. Bottom spacer 12 is constructed in a similar manner as top spacer 11.

Referring now to Fig. 3, there is shown an electrode asembly, as illustrated in Fig. l, with the addition of a tensioning device 23 electrically connected to the upper tab extending from suppressor grid 14. Fig. 3 shows filament wires 24 terminating in a tab 25 which is electrically connected to one end of tensioning device 23. Located below bottom spacer 12 is a tab structure 26 electrically connected at one end to filament wires 24 and connected at the other end to an extension of suppressor grid 14. In tubes of this type, it has been found most desirable to use one suppressor grid as the electrical terminating point for the upper end of the filament wire and the other suppressor grid as the lower electrical terminating point for the filament wire, thereby reducing the necessity for adding separate contacting pins for the filament circuit. In this stage, filament wires 24 are located Within control grid wires and within the central opening in both the upper spacer 11 and the lower spacer 12, as shown by the cutaway in spacer 11.

Referring now to Fig. 4, there is shown an electrode subassembly in the next stage of assembly which now includes the addition of half spacers 27 adjacent to and outboard of upper spacer 11 and half spacer 28 adjacent to and outboard of lower spacer 12. Half spacers 27 and 28 are constructed identical in shape and both have the necessary openings for allowing the projections of anode 13 and suppressor grid 14 to be extended therethrough, and similarly spacer 28 has openings for the extensions of suppressor grid 14' and anode 13 to extend therethrough. In locating filament wires 24, it should be remembered that the critical dimension is with respect to the vertical posts 18 and 19 supporting the screen grid and the control grid respectively. The straight edge 29 of half spacer 27 and the straight edge 36 of lower half spacer 28 are constructed to be on a center line extending through vertical grid posts 18 and 19. It can be appreciated that placing the center line 29 of upper half spacer 27 on the center line with the vertical grid posts will thereby actually place grid wires 24 at a point slightly off the center line due to the thickness of the filament wires. This slight deviation is realized and corrected by the placement of lower half spacer 28 diagonally opposite upper half spacer 27, as shown in Fig. 5. By bending upper tensioning device 23 and lower tab support 26 in such a manner that filament wires 24 contact the straight edge 29 on upper half spacer 27 and straight edge St on lower half spacer 2%, the filament wires 24 are actually placed on a small diagonal running from upper right to lower left which passes at the center as illustrated. Considering the filament size and the allowable tolerances on the spacer die that produces the main spacer, it has been found more advantageous to place the filament on a small diagonal rather than attempt to make the filament vertical.

Referring now to Fig. 5, there is shown a top view in a greatly exaggerated form of the electrode structure shown in Fig. 4. Fig. shows the placement of upper half spacer 27 against upper spacer 11 and how half spacer 27 abuts against vertical grid supports 18 and vertical supports U, which thereby accurately locates straight edge 2? on the center line extending through said vertical grid supports.

Referring now to Fig. 6, there is shown a completed electrode subassembly 'within a glass envelope 31, which electrode assembly now includes a getter and support 32 and leads 33 for providing electrical contact to the various components of said electrode assembly.

This completes the description of the embodiment of the invention illustrated herein. However, many modifications and advantages thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, it is entirely conceivable that, for certain applications, only a single half spacer need be used and, further, for larger tubes where extreme accuracy and placement of the filament wires is required, it is entirely possible to offset the straight edge of the half spacer and thereby compensate for the thickness of the filament wires for placing the center line of said filament wires on the same line through the vertical grid support posts. Accordingly, it is desired that this invention not be limited to the particular details of the embodiments disclosed herein except as defined by the appended claims.

What is claimed is:

1. An electron discharge device comprising at least a filament having filament connectors attached to the ends thereof, and a grid which is wound around posts supported by a plurality of insulating main spacers disposed within an evacuated envelope, said device having extremely close grid-to-filament spacing, a central opening in each of said main spacers of sufiicient size to allow said filament and connectors to pass therethrough, and at least one insulating half spacer positioned adjacent to a main spacer and having a straight edge portion covering part of the central opening in said main spacer to which it is adjacent, said straight edge being positioned substantially along a diametral line of said grid winding, said straight edge further being in pressure contact with said filament whereby said filament is maintained substantially equidistant between opposing control surfaces of said grid winding.

2. An electron discharge device comprising at least a filament having filament connectors attached to the ends thereof, and a grid which is wound around posts supported by a plurality of insulating main spacers disposed within an evacuated envelope, said device having extremely close grid-to-filament spacing, a substantially rectangular central opening in each of said main spacers of suflicient size to allow said filament and connectors to pass therethrough, and at least one insulating half spacer positioned adjacent to a main spacer and having a straight edge portion covering part of the central opening in the main spacer to which it is adjacent, said straight edge being positioned substantially along a diametral line of said grid winding, said straight edge further being in pressure contact with said filament whereby said filament is maintained substantially equidistant between opposing control surfaces of said grid winding.

3. An electron discharge device comprising at least a filament having connectors attached to the ends thereof, and a grid which is wound around posts supported by a pair of insulating main spacers disposed Within an evacuated envelope, said device having extremely close grid-tofilament spacing, a central opening in each of said main spacers of suflicient size to allow said filament and connectors to pass therethrough, and a pair of additional insulating half spacers one of each of which is positioned adjacent to a different one of said main spacers, said half spacers each having a straight edge portion covering part of the central opening in the main spacer to which it is adjacent, each of said straight edges being positioned substantially along a diametral line of said grid winding and further being in pressure contact with opposing surface areas of said filament whereby said filament is maintained substantially equidistant between opposing control surfaces of said grid, each of said half spacers further being positioned on the outboard side of a difierent one of said main spacers.

4. An electron discharge device comprising at least a filament having connectors attached to the ends thereof, and a grid which is wound around posts supported by a pair of insulating main spacers disposed within an evacuated envelope, said device having extremely close grid-tofilament spacing, a central opening in each of said main spacers of suflicient size to allow said filament and connectors to pass therethrough, and a pair of additional insulating half spacers one of each of which is positioned adjacent to a different one of said main spacers, said half spacers each having a straight edge portion covering part of the central opening in the main spacer to which it is adjacent, each of said straight edges being positioned substantially along a diametral line of said grid winding and further being in pressure contact with opposing sur- (face areas of said filament whereby said filament is maintained substantially equidistant between opposing control surfaces of said grid, each of said half spacers further being positioned on the outboard side of a different one of said main spacers on diagonal sides.

References Cited in the file of this patent 

